1. Field of the Invention
The present invention relates to a photopolymerizable composition for use in a monochrome or polychrome (multicolor) recording material and recording process which can utilize a light source falling within an ultraviolet to infrared region. More specifically, the present invention relates to a photopolymerizable composition exhibiting improved sensitivity, storability, fixability by light, decolorization of organic dyes, etc., and to a recording material and a recording process using the photopolymerizable composition.
2. Description of the Related Art
Heretofore, dry-type image-recording processes, which do not use a liquid developing solution or the like and do not produce waste, have been studied. Among these processes, a process using a composition that hardens by light is drawing attention.
According to this process, when a recording material is exposed to light, a composition, hardenable by the action of light and contained in an exposed portion of the recording material, is hardened and thus a latent image is formed. Meanwhile, a component, which is to be involved in a coloration or decolorization reaction when heated and is contained in an unexposed portion of the recording material, moves within the recording material so that a color image is formed. When a recording material according to the above-described process is used, a visible image is formed by irradiating the recording material with light through an image original so that the portion exposed to light is hardened and a latent image is formed and thereafter heating the recording material so that a component, which is to be involved in a coloration or decolorization reaction and is contained in an unhardened portion (i.e., unexposed portion), moves.
According to this process, it is possible to realize a perfectly dry system that produces no waste.
Specifically, there are several kinds of recording materials as the recording materials to be used according to the above-described process. This process is useful for recording color images in particular, although this process is a characteristic one also as a recording process for black-and-white images. Known as a specific recording material is, for example, the two-component, photo- and heat-sensitive, color-forming recording material disclosed in Japanese Patent Application Laid-Open (JP-A) No. 52-89915. This is a heat-sensitive, color-forming recording material which uses, for example, an electron-accepting compound and an electron-donating, colorless dye as the two components and contains a photo-hardenable composition either inside or outside microcapsules or both inside and outside microcapsules.
However, in this recording material, even if the photo-hardenable composition inside microcapsules is fully hardened, the coloration in the hardened portions cannot be sufficiently inhibited. Because of this, non-image portions are colored and contrast tends to decrease.
Known as a recording material whose non-image portions are free from coloration is, for example, the recording material which is disclosed in JP-A No. 61-123838 and produced by laminating a layer containing a composition consisting of a vinyl monomer having an acidic group and a photopolymerization initiator, an isolating layer, and a layer comprised of an electron-donating, colorless dye.
This recording material is associated with the problem that the density of developed color itself is relatively low, although non-image portions, i.e., the portions hardened by a photopolymerization reaction, are free from coloration because the thermal diffusion of the acidic group does not occur in the non-image portions.
JP-A No. 60-119552 discloses a recording material which provides a negative-type image by a similar process. In this recording material, a photopolymerizable composition, which comprises of a monomer or prepolymer designed to bleach a dye and a photopolymerization initiator, and a dye, which is to be bleached by a monomer or prepolymer, are isolated from each other. This recording material is also associated with the problem that the density of developed color itself is relatively low, although non-image portions are free from coloration as in the case of the recording material described above.
In view of the problems described above, the present applicant has proposed the recording material described in JP-A No. 3-87828 and the recording material described in JP-A No. 4-211252 as recording materials capable of decreasing the coloration in non-image portions and providing a high image density. The former recording material is characterized in that one of the two components in the two-component, photo- and heat-sensitive, color-forming recording material is enclosed in microcapsules while the other component is present as a hardenable compound of the photopolymerizable composition or is present together with the photopolymerizable composition outside the microcapsules. The latter recording material is a photo- and heat-sensitive recording material having a layer containing microcapsules enclosing an electron-donating, colorless dye and a photo-hardenable composition comprising of an electron-accepting compound, a polymerizable vinyl monomer, and a photopolymerization initiator outside the microcapsules.
Recording of color images in the photo- and heat-sensitive recording materials described above can be achieved by using a recording material comprising a support having laminated thereon plural recording layers each of which is sensitive to a different wavelength and forms a different color.
An example of multicolor photo- and heat-sensitive recording materials is the photo- and heat-sensitive recording material previously proposed by the present applicant. More specifically, examples thereof include a multicolor photo- and heat-sensitive recording material comprising plural recording layers each of which is sensitive to a different wavelength and forms a different color. That is, the multicolor photo- and heat-sensitive recording material is produced by laminating a first recording layer which is sensitive to the light having a central wavelength of λ1 and develops (forms) a color, an intermediate layer which absorbs the light having a central wavelength of λ1, a second recording layer which is sensitive to the light having a central wavelength of λ2 and develops a color different from the color of the first recording layer, . . . , an intermediate layer which absorbs the light having a central wavelength of λi−1, and an i th recording layer which is sensitive to the light having a central wavelength of λi and develops a color different from the colors of the first, second, . . . , and (i−1) th recording layers, in that order in the direction of the support from the light source for exposure, wherein i is equal to or greater than 2 and the central wavelengths have the relationship of λ1<λ2< . . . λi. For example, i may be 3, 4, 5, 6 or 7. Further, the i th recording layer is formed on the support. this construction of the multicolor photo- and heat-sensitive recording material may be used in the present invention.
These recording materials can be used in various applications, but, when these recording materials are used, a light source that enables the image recording was limited to UV light or shortwave visible light and the use of a small-sized, inexpensive infrared laser or blue to red light was impossible.
In order to enable more rapid and finer image formation, a dye or the like, whose absorption wavelength falls within the ultraviolet to infrared region of the irradiation light, needs to be introduced into the recording layer when the small-sized, inexpensive infrared laser or blue to red light is used. However, if a dye or the like, particularly a dye or the like whose absorption wavelength falls within a visible light region, is used, the background is colored and the images to be obtained necessarily have a low contrast and poor quality. On the other hand, the use of a dye or the like whose absorption wavelength falls within a near-infrared region diminishes the coloration of the background. But in this case, the problem is that the laser required is expensive.
Meanwhile, examples of pressure-sensitive, color-forming recording materials include the photo- and pressure-sensitive, recording materials disclosed in U.S. Pat. No. 4,399,209, U.S. Pat. No. 4,440,846, and others. In these recording materials, a colorant precursor as an image former is enclosed in microcapsules and, after image-wise exposure, the microcapsules in the portions that have not undergone photo-hardening are broken by the application of a uniform pressure. As a result, the colorant precursor released from the microcapsules reacts with the developing agent present outside the microcapsules and thus visualization is performed. Examples of these multicolor recording materials include the recording materials described in U.S. Pat. Nos. 4,842,976 and 4,576,891.
However, also in these recording materials, like the photo- and heat-sensitive recording materials described above, almost all compositions to be photo-hardened have sensitivity only to shortwave light, and a light source that enables the image recording was limited to UV light or shortwave visible light. Therefore, the use of a small-sized, inexpensive infrared laser or blue to red light was impossible.
Another problem was that, in order to enable more rapid and finer image formation, it was inevitable that the background was colored and the images obtained had a low contrast and poor quality.